Thanks! I haven't used this macro in a billion years and wrote it as a comfort thingie for the first 100 project Euler problems.
This thread got me to start thinking about how to memoize "smarter" and having a macro that allows you to trade a bit of speed for being able to specifically memoize the last n or the most common n arguments. -- Linus Björnstam On Sun, 12 Jan 2020, at 04:03, Christopher Lam wrote: > I can add a contribution! The good thing about memoize is it's simple > to create. You forgot a catch however: if the memoized return-val is #f > then your memoizer > https://hg.sr.ht/~bjoli/misc/browse/default/memoize.scm will not > recognise that #f is a valid cached return-val and will call the lambda > again. (FWIW I shudder think what a *fast* memoizer would do). > > Here's how I did mine: > > (define (memoize f) > (let ((h (make-hash-table))) > (lambda args > (cond > ((hash-ref h args) => car) > (else (let ((res (apply f args))) > (hash-set! h args (list res)) > res)))))) > > (define-syntax-rule (lambda/macro args body ...) > (memoize (lambda args body ...))) > > (define-syntax-rule (define/macro (f . args) body ...) > (define f lambda/macro args body ...)) > > > > On Sat, 11 Jan 2020 at 17:40, Linus Björnstam > <linus.inter...@fastmail.se> wrote: > > I have a macro called lambda/memo and define/memo for these situations: > > https://hg.sr.ht/~bjoli/misc/browse/default/memoize.scm > > > > If the function gets called with a gazillion different arguments the > > memoizatiin hash gets large, and there are no mechanisms to stop that from > > happening. It also lacks a fast path for single argument functions. > > > > You can disregard the repo license. Use that function is you like, if you > > like to. > > > > > > -- > > Linus Björnstam > > > > On Fri, 10 Jan 2020, at 23:36, Linas Vepstas wrote: > > > So, I've got lots of C code wrapped up in guile, and I'd like to declare > > > many of these functions to be pure functions, side-effect-free, thus > > > hopefully garnering some optimizations. Is this possible? How would I do > > > it? A cursory google-search reveals no clues. > > > > > > To recap, I've got functions f and g that call into c++, but are pure > > (i.e. > > > always return the same value for the same arguments). I've got > > > user-written code that looks like this: > > > > > > (define (foo x) > > > (g (f 42) (f x) (f 43)) > > > > > > and from what I can tell, `f` is getting called three times whenever the > > > user calls `foo`. I could tell the user to re-write their code to cache, > > > manually: viz: > > > > > > (define c42 (f 42)) > > > (define c43 (f 43)) > > > (define (foo x) (g c42 (f x) c43)) > > > > > > but asking the users to do this is .. cumbersome. And barely worth it: > > `f` > > > takes under maybe 10 microseconds to run; so most simple-minded caching > > > stunts don't pay off. But since `foo` is called millions/billions of > > times, > > > I'm motivated to find something spiffy. > > > > > > Ideas? suggestions? > > > > > > -- Linas > > > -- > > > cassette tapes - analog TV - film cameras - you > > > > >